1. Field of the Invention
The present invention relates to a method for image formation, wherein a color image, a light transparent image, and a light transparent protective layer are formed on an object by using an intermediate transfer recording medium comprising a substrate and a light transparent protective layer provided on one side of the substrate, a first thermal transfer recording medium comprising a substrate and a light transparent ink layer provided on one side of the substrate, and a second thermal transfer recording medium comprising a substrate and, provided on one side of the substrate, a color ink layer comprising a thermoplastic resin and a colorant. The present invention relates also to an image formed object produced by the method for image formation.
2. Prior Art
Thermal transfer can easily record variable information and thus is extensively used in a wide variety of applications. The thermal transfer is a method which comprises the steps of: putting a thermal transfer film, comprising a colorant layer provided on a substrate, on top of an object optionally provided with a receptive layer; pressing the assembly between a heating device, such as a thermal head, and a platen roll; and selectively heating the heating device in its heating portion according to image information to transfer the colorant contained in the colorant layer on the thermal transfer film onto the object, whereby an image is recorded on the object. Thermal transfer methods are roughly classified into thermal ink transfer (hot melt-type thermal transfer) and thermal dye sublimation transfer (sublimation-type thermal transfer).
The thermal ink transfer is a method for image formation wherein a thermal transfer film bearing thereon a heat-fusion ink layer is heated by the above heating means and the component of the softened heat-fusion ink layer is transferred onto an object such as natural fiber paper or plastic sheet to form an image. The heat-fusion ink layer used herein is formed of a dispersion of a colorant, such as a pigment, in a binder, such as heat-fusion wax or resin and is supported on a substrate such as a plastic film. The formed image has high density and high sharpness, and this method is suitable for recording binary images such as characters and line drawings.
On the other hand, the thermal dye sublimation transfer is a method for image formation wherein a thermal transfer film bearing thereon a sublimable dye layer is heated by the above heating means to sublimate and transfer the sublimable dye contained in the dye layer onto a receptive layer provided on an object, whereby an image is formed on the object. The sublimable dye layer used herein is formed of a solution or dispersion of a sublimable dye used as the colorant in a binder resin and is supported on a substrate film such as a plastic film. According to this method, since the amount of the dye transferred can be regulated dot by dot according to the quantity of energy applied to a heating device, such as a thermal head, the reproduction of gradation can be realized by varying the density.
Thus, the thermal ink transfer method and the thermal dye sublimation transfer method have respective features, that is, the thermal ink transfer method can easily and clearly form images of characters, numerals and the like, while the thermal dye sublimation transfer method is excellent in gradation rendering and can form images such as a photograph-like image of a face in a faithful, clear manner.
Images formed by the above thermal transfer methods, independently of whether the images have been formed by the thermal ink transfer method or the thermal dye sublimation transfer method, are unsatisfactory in fastness or resistance properties such as abrasion resistance, lightfastness, and alteration preventive properties. To cope with the unsatisfactory fastness or resistance properties, a protective layer has hitherto been formed on the image. For example, Japanese Patent Laid-Open No. 159795/1991 describes that information such as images and characters are formed on a card substrate and a transparent protective layer is provided on at least a part of the surface of the information. In this case, for example, two or more protective layers are transferred so that they overlap with each other and are different from each other in transfer area. At least one of the protective layers contains a brightening agent and/or an ultraviolet absorber. In this method, however, since the transfer of the protective layer onto the object (card) is carried out twice or more, damage to the object is large. Further, the number of steps (transfer) necessary for preparing a print is large, and a great deal of time is required. Therefore, for example, a deterioration in print quality and an increase in production cost are disadvantageously likely to occur.
Japanese Patent Laid-Open No. 177249/2000 describes a record produced by forming a color image on recording paper and forming a transparent image of a transparent ink on the color image and further discloses that an overcoat is formed between the color image and the transparent image. The claimed advantage of the record is to improve the weathering resistance and abrasion resistance of the color image and to permit the transparent image on the color image to be viewed by the reflection of light according to the angle of the line of sight to the transparent image recorded face. Also in this case, however, since the transfer onto the color image on the recording paper is carried out a plurality of times, that is, since the transparent image and the overcoat are transferred onto the color image on the recording paper, damage to the object is significant. Further, the number of steps (transfer) necessary for preparing a print is large, and a great deal of time is required. Therefore, for example, a deterioration in print quality and an increase in production cost are disadvantageously likely to occur.
The present invention has been made with a view to solving the above problems of the prior art, and it is an object of the present invention to provide a method for image formation which can produce an image formed object possessing excellent fastness or resistance properties such as excellent abrasion resistance, lightfastness, and alteration preventive property, is less likely to cause damage to an object, is free from a deterioration in quality of the image, and does not incur an increase in production cost, and to provide an image formed object.
The above object can be attained by a method for image formation, comprising the steps of: providing an intermediate transfer recording medium comprising a substrate and a light transparent protective layer provided on one side of the substrate; providing a first thermal transfer recording medium comprising a substrate and a light transparent ink layer provided on one side of the substrate; putting the intermediate transfer recording medium and the first thermal transfer recording medium on top of each other so that the light transparent protective layer in the intermediate transfer recording medium faces the light transparent ink layer in the first thermal transfer recording medium; imagewise heating the assembly to form a light transparent image on the light transparent protective layer in the intermediate transfer recording medium; providing a second thermal transfer recording medium comprising a substrate and, provided on one side of the substrate, a color ink layer comprising a thermoplastic resin and a colorant; putting the intermediate transfer recording medium with the light transparent image formed thereon on top of the second thermal transfer recording medium so that the light transparent protective layer on its light transparent image-formed side in the intermediate transfer recording medium faces the color ink layer in the second thermal transfer recording medium; imagewise heating the assembly to transfer the color ink layer or the colorant contained in the color ink layer onto the light transparent protective layer on its light transparent image-formed side in the intermediate transfer recording medium, whereby a color image is formed on the light transparent protective layer; putting an object on top of the intermediate transfer recording medium with the light transparent image and the color image formed on its light transparent protective layer so that the light transparent image and the color image face the object; and heating the whole assembly to form a color image, a light transparent image, and a light transparent protective layer on the object.
According to the present invention, there is provided an image formed object comprising an image formed by the above method for image formation.
In the image formed object according to the present invention, the thickness of the light transparent image is preferably 0.3 to 5.0 xcexcm.
The light transparent protective layer is preferably composed mainly of a thermoplastic resin having a glass transition point of 50 to 120xc2x0 C.
Preferably, the thermoplastic resin is at least one member selected from a polyester resin having a number average molecular weight of 2000 to 30000, a vinyl chloride-vinyl acetate copolymer having an average degree of polymerization of 150 to 500, and a homopolymer or copolymer, of a methacrylate monomer, having a weight average molecular weight of 20000 to 80000.
Preferably, the light transparent ink layer for the formation of light transparent image is composed mainly a thermoplastic resin having a glass transition point of 50 to 120xc2x0 C.
Preferably, the thermoplastic resin is at least one member selected from a polyester resin having a number average molecular weight of 2000 to 30000, a vinyl chloride-vinyl acetate copolymer having an average degree of polymerization of 150 to 500, and a homopolymer or copolymer, of a methacrylate monomer, having a weight average molecular weight of 20000 to 80000.
Preferably, both the light transparent ink layer, for the formation of the light transparent image, and the light transparent protective layer contain respective thermoplastic resins, and the thermoplastic resin contained in the light transparent ink layer and the thermoplastic resin contained in the light transparent protective layer are analogous to each other in polymer structure and each have an ester linkage in its molecular structure.
The image formed object according to the present invention is produced as follows. An intermediate transfer recording medium comprising a substrate and a light transparent protective layer provided on one side of the substrate, and a first thermal transfer recording medium comprising a substrate and a light transparent ink layer provided on one side of the substrate are first provided. The intermediate transfer recording medium and the first thermal transfer recording medium are put on top of each other so that the light transparent protective layer in the intermediate transfer recording medium faces the light transparent ink layer in the first thermal transfer recording medium. The assembly is imagewise heated to form a light transparent image on the light transparent protective layer in the intermediate transfer recording medium. The intermediate transfer recording medium with the light transparent image formed thereon is then put on top of a second thermal transfer recording medium comprising a substrate and, provided on one side of the substrate, a color ink layer comprising a thermoplastic resin and a colorant so that the light transparent protective layer on its light transparent image-formed side in the intermediate transfer recording medium faces the color ink layer in the second thermal transfer recording medium. The assembly is imagewise heated to transfer the color ink layer or the colorant contained in the color ink layer onto the light transparent protective layer on its light transparent image-formed side in the intermediate transfer recording medium, whereby a color image is formed on the light transparent protective layer. An object is then put on top of the intermediate transfer recording medium with the light transparent image and the color image formed on its light transparent protective layer so that the light transparent image and the color image face the object. The whole assembly is heated to form a color image, a light transparent image, and a light transparent protective layer on the object.
In the image formed object thus obtained, the image formed by the transfer of the color ink layer is protected by the light transparent protective layer and, further, by virtue of a combination thereof with the light transparent image, has excellent fastness or resistance properties such as excellent abrasion resistance, lightfastness, and alteration preventive properties. Further, for example, according to the angle of the line of sight to the image-recorded face in the image formed object, the convex portion in the light transparent image transferred to the object is legible by the reflection of light.
Further, a protective layer having on its surface a color image and a light transparent image can be formed on an object by single transfer operation using an intermediate transfer recording medium comprising a light transparent protective layer having on its surface a color image, formed by the transfer of a color ink layer, and a light transparent image formed by the transfer of a light transparent ink layer. Therefore, the damage to the object by the transfer operation is less likely to occur, and a deterioration in image quality and an increase in production cost can be suppressed.